There are no code available for the nRF51822 that would enable you to using AT commands. We have app_trace functionality that will print debug information from various code examples. We have serialized the functions related to the softdevice, so you can control the softdevice and hence the Bluetooth functionality through UART, but it's a proprietary implementation, not the same as AT commands.
As answered already which is a fact. But to make this happen, the way arduino and any other bluetooth 2 module use to behave, for that to replicate with nrf51822, you have to write firmware for this SoC and make an arrangement to interface with arduino, say with serial or with spi or such.
So the SoC firmware should understand commands, (you will say as AT Commands). Hence, you have to make, decide AT Commands which may be according to you, then integrate it with arduino .
